Echo-suppressing and energy-limiting circuits



H. w. ONEILL 1,788,736

ECHO SUPPRESSING AND ENERGY LIMITING CIRCUITS Jan. 13, 1931.

Filed Feb. 2, 1927 2 Sheets-Sheet 1 Jan, 13, 1931. H, w, o 1,788,736

ECHO SUPPRESSING AND ENERGY LIMITING CIRCUITS Filed Feb. 2, 1927 2 Sheets-Sheet 2 by A9 I f/omey Patented 1a.. 13, 1931,

HEN 1tY'w.oNnILt, or ELMHURST,'1\TEW YoraK, nssirenoa'ro anti. 'r 'ntnrn'jonnle LABORATORIES, mooaroanrnngornnw ORK, n; Y,, Al CORPORATION on NEW,

QYoRK This invention relatesto Wave transmission systems and particularly to two-Way signaling transmission systems.

An obyec't of the invention is to'provide a simple echo suppresslng circuit.

v vide .a' simple circuit arrangement for limit ances are produced by these echoes, which 'ing the'energyitransmitted over a circuit.

,Another object of the invention is to provide acombined echosuppressing and energylimiting circuit.

In long; distance telephone systems employing repeaters, particularly those in which the repeaters are adjusted to give high 5" gains, objectionable echo effects are sometimes encountered due to reflection points on the side of the repeater remote from the speaker, whereby the echoes are highly am-' piified'. all similar 'efiect which-is'ordinarily 20 more pronounced'is due to imperfections in balancing atthe repeater on thesi-de remote from the speaker. Ob ectionable disturbmay be accentuated'bysudden increases of energy due to abnormal stress of Words or syllables in speaking, inadvertent striking of: a transmitter, side tone efiects from extraneous-noises, surges due to switch hook manipulations, and the like. These abnormally fect transmission by producing acoustic shock and confusion in the ear of the listeningparty. T a

Circuit arrangements forreducing the ethciency of transmission in onefdirection While Waves are being transmitted" in the other direction have been used to'limittheecho eifects. Other arrangements have been used to'automatically limitthe direct effectat the receiver of sudden increases'of transmitted energy. a i a Y In its preferred embodiment, this invention, specifically stated, consists of a two way signaling system employing repeaters of the fourwire type-that is, the type in-Which the repeating path in one direction utilizes one pair of line Wires and the repeating path inthe opposite direction a'second pair of line i sion and wires, the two repeating paths being associated With each other and w th the two-way 'highenergy conditions may also directly af J ncno-surrnnssme AND'nnERGYmIMiTIitGcriaotrirs Application filed February 2, 927. serial-no. 165,283. g

transmission circuit by abridge connection. e navinga v bratory relay operated by Waves I in the output of the amplifier at the terminal of ea-ch one-Way line. Eacho'f these relays it o is responsivelto the amplified aves in the Another object of the invention is to pro path to which it is connected to control-aresistance inthe oppositely directedvpath for reducing theefiiciency oftransmission of that, patln'thus reducing troublesome echo effects, Each of these relays also 1s made marginally responsive tofun'amplified Waves of abnore mally high-energy levels,- which.i.in usual ar rangements are dissipatedin the amplifieroutputcircuit, to limit the energy transmitted through the opposite pat-h; Thus when JVaYGS are transmittedin one directiomz-the relay inone'path acts asan echo suppressor. 1

and therelay in the-other pathas an energylimiter, and When'transmission takes place in the opposite direction the functionsof the twor'elaysare reversed.

The relays are preferably'of device, also, may berfound useful inother- Wavesto traverse the "echo path. The same hold ov'ereffect: may be produced by arranging the relaytoreducethe cathode'heating current or the repeater not in use. The effi ciency' of this' repeater will not 'belrestored to normal for "some time due to the'time required for the cathode to .heat'up again. This"invention can be more readily understood by reference'to the following detailed description in connection with the drawing, inwhich: I

V Fig. 1 shows a four-Wire transmission sys tem embodying the combined echo suppres I energy limiting circuit of in vention;

p the high speed type capable of vibrating atspeech frequen nje'ct'efjd togetlier 'tliroi igh one-way transmis sion lines 12' and '13 by means of the usual hybrid or balanced transformer arrangements. Transmission takes place in the-lines 12 and 13 in the directions indicated by the arrows. Terminal repeaters 14, 15, 16, and 17 are provided for; the lines 12 and 13-, re-

spectively. Each of these lines maybe pro vided with intermediate repeaters if the conditions so require; Connected across a condenser 18 associated with the output transformer 19 of repeater 15 in line12 are the windi'n s of a' vibratory relay 20 which is prefera ly ofthe type described in ONeill ing a loose contact member vibrated in reatents No. 1,603,289 of October 19, 1926, and No. 1,607,910 of November 23, 1926, havspon'sc to-signalwaves. The contacts of this relay are connected so as normally to shortcircuit a resistance 21 connected tothe primary'winding ofthe input transformer 22 of the repeater 17 in line 13. The winding of a second vibrator relay 23 is connected to the output transformer 24 of the repeater 16 in line 13 across a similar condenser 25. The contacts of this relay normally short circuit a resistance 26 connected to the primary winding of the inp'ut transformer 27 of the repeater 14 in line 12. 1 Y

\Vaves transmitted from line in the direction from west to cast, for example, are divided between the circuits of repeaters 14 and 16'by the associated balanced transformer, one portion being dissipated in the output circuit of the repeater 16 and the other portion being amplified by repeaters 14 and and impressed on the 'line 11 through the other balanced transformer. These amplified waves inthe output transformer 19 of repeater 15 energize the relay 'toopen the short circuit around the resistance 21 and thereby reduce. the efliciency of transmissionthrou-gh the oppositely directed path includingamplifiers 17, 16 and line 13. The relay 23 :is so adjusted th-atit will not be operated by waves of normalenergy from line 10. However, if the energy level of the waves exceeds a certain predetermined value, relay 23 will operate to open the short-circuit around resistance '26 in the main transmission path and lower the efiiciency of trans mission through the circuit including amplifier 14. In this way the energy level of the w'aves'transmitted is'main'tained below this predetermined value. For transmission in the opposite direction, the functions of relays 20 and 23 are interchanged.

Since the relays are made responsive to amplified wavesfor suppressing echo efiects and to unamplified waves for accomplishing the energy limiting function, they may be readily adjusted to selectively respond to produce both eifects. The amount of loss introduced bytheresistances 21 and 26 must be'sufficient to prevent any appreciable quan= 'tity of energy, which'due to residual unbalances in the associated balanced transformer may be impressed on the respective one-way line from the other, from traversing that line and setting up echo effects.

Relays of the vibratory type described in the above mentioned patents may be made responsive to any frequencies in the voice range. Since these relays require little energy for their operation the condensers v18 and may he of relatively large capacity c'ausi'ng little loss in the associated circuits.

The response of this type of relay is practically synchronous with the impressed waves so that delay circuits to retard the returning waves are not required.

Fig. 2 shows an alternate method of connecting the relays to the transmission circuits, shown in this figure, the winding of relay 23 is connected to the tertiary winding 28 of the output transformer 24. Since the relays are very sensitive. this tertiary windingfmay have only afew turns so that practically no loss will be introduced by its.

use. In cases where a monitoring winding is used the relay winding may be designed to have a high impedance and to be bridged across themonitoring winding without the introduction of appreciable loss.

While the circuits o-fIFigs. 1 and 2 illustrate the invention embodied in four-wire repeater circuits employing one-way trans mission lines of considerable geographic extent, the invention is also applicable to other type o-fcircuits, for example the ordinary two-way two-element (22 type) repeater rcu I Fig. 3 shows a transmission system employin'g two two-way transmission lines 31 and 32 connected togetherby means of a four-wire transmission circuit associated with the lines 31 and 32 through the usual balanced transformer arrangen'ient; Transmission takes place in the directions indicated by the arrows. Waves are transmitted ,from west to east through the terminal repeater 33, line 34, intermediate repeater 35, line .36, terminal repeater 37 to the line 32, and in the opposite direction through the terminal repeater 38, line 39, intermediate repeater 40,1ine 41, terminal repeater 42 to the line 31.

lOO

"The intermediate repeater comprises a vacuum amplifier tube 43, an input transformer 44 and an output transformer 45. The

intermediate repeater similarlyemploys a vacuum tube amplifier t6, an inp ut'trans former 47; and at outputgtransformer 48 *The'windings of a vibratory relay" 49 ofisim-' ,waves belng transrnltted from west to east ilar type to those employed in the circuit of Fig. l are connectedjacross axcondenser 50 associated with the' secondary Winding of the output tra1'1sformer45.- The contactsof relay 49 are arranged to normallvfshort circuit a resistance, 51 associated with the 1 primary winding of the input transformer 4,7, This resistance maybe of such value as to com-f 'pletely'incapacitate the amplifier when the short circuit is opened. The windings of a vsimilar relay 52 are connected to a condenser :33' associated with the secondary winding of the output transformer 48. The contacts of this relay are arranged-to normally short-- circuit a resistance 54 associated with the primary'winding of the input transformer 4-1. The relay 49 isactuated by the amplified v to open the'short-circuit around resistance 51 and reduce the transmission eficiency of the repeater &0. In this way the energy transmitted'over the east to west line due to waves impressed thereon from'the west to east line as a result of unbalances in the balanced transv former circuit is prevented from attaining i such a level as W111" produce serious echo nathfromthe repeater to repeater 40.

effects. Relay s9 is so designed that itsvibration is undamped s'o that the efliciency of the repeater lO Wlll remain low for the-t mers quired tor the echoc'urrents'to traverse the Relay52 acts in the same manner for trans- 1 mission from east to West.

Fig. 4t shows an alternative arrangement for perit'orming the same function as the arrangement oi Fig. 8. In this embodiment the relay 59 is similar to the relay d9 except that its vibration may be damped. The windings,

ofthi's relayare connected in the saine way to the condenser butlthe contacts 'areconnected to normally short-circuit areslstance 50 connected in the cathode heating circuit of the tube 46. Whenthe relay 59 1S operated toopen theshort-circuit around the resistance (50 the amplification of the tube 46 will be lowered and will remain at this lower value i for a considerable time after the contacts of relay 59 are closed, due to the time required for the cathode of the tube 46 to heat up to a point where its emission is again normal.

Relay 62 is similarly arranged' -to normally i short-circuit resistance 63 connected in the cathodeheating circuit of the tube .43, and

, iwhenoperated to open the short circuit so as to decrease the cathode heating current of tube 43 and thus the'amplifi'oation produced bythat tube.

VVhat is claimed is:

1. In combinationin a signaling system, a

two-Way. signal transmission circuit two o-ppositely directed (eastward and Westward), one-way signal transmlssion paths connected 7 energy r vel-of theeastward waves exceeds mission circuits; a pair of one-way trans. mission circu ts connected between said twobeingfalso marginally-operated to reduceth theretoso thatieastward si'gnal wa-vesiiizsaid o two-way 'circuita divide between: saidlritt o '7 pathsc marginally operating means in the westward, path-responsiveto the receivedeas'tward waves toreduce the 'transmission efiiciency of the eastwardgpath when the;

certain level above the .normalr signali In combination,:a tw'owvay .transmi'ssfm v sion circuit,: a pair of one-way transmission; circuits, means for connectlngsald one-way; v circuits in con ugate relatlon' to said twosway circuit-wherebywaves-from saidltwo-I WayCII'CLHiT d -vlde between saldone-wayzcir-j cuits to be transmittedbyone and dissipated i-nli the zotheryiand means [controlled by the energy levelof the waves in said OCllGlfiOIl: way circuit tolfcontrol the efficiency of trans mission throughsaid first one-way circuit w a c c .7 Q5: In 'comblnatlon, a tWo-wayitransnnsr l si'on circuit, a pair of one-way tra-lnsmissionv Waycircuits, a repeater in each of. said "oneway circuits, means responsive to waves inone of said one-way circuitsfor reducing the eihciency of transmission through the-other. of'said one-way circuits while waves are be-Q ing transmitted throughsaid firstlone-way circuit, said means being also. marginally ops; erated toreduce the efficiencygof transmission of said other one-way circuit when the energy of the waves-impressed on saidotheroneway circuitisabove'a certain levehandlneans similarly responsive to waves in: said other I one-way circuit, a i 7 5. In combination, two two-way transmis, l sion'circuit's pair of one-way transmissi circuits; connected between said two-way ci -cuits, a one way repeat-er ineach ot'saidoneway circuits, .rrieans responsive: to-waves :in

'theIoutputofthe repeater in one or said cire f cuits'forreducingtheetficiency of transmise I sion throughlthe other oi' said one-waycircuits while Waves are beingtransmitted through said first one-waycirciut, saidmean efficiency of transmission'of said othenjone c way circuit when the energy, of the waves pressed thereon from the associated twoay circuit isla'bove, a, certain level, and me similarly responsive to waves the 1 output of the repeater in the other one-way circuit.

*6. In combination in a signaling system, two two-way transmlssion lines, a pa1r of ;one-way transmission lines, means for connecting one terminal of each of said one-way lines in conjugate relation to each of said 13W0' way lines, respectively, whereby signalwaves from one of said two-waylines divide between said one-way lines to be transmitted by one anddissipated in the other and waves from the other of said two-way lines divide between said one-way lines to be transmitted by said other one-way line and dissipated in said one one-way line, a repeater in each of said one-way lines, marginally operated means reto signal waves in said other one-way line.

Y 7. In combinationin a signaling system, two two-way transmission circuits, :1 pair of one-way transmission circuits, means for connecting one terminal of each of said one-way circuits in conjugate relation to each of said two-way circuits, respectively, whereby signal waves from one of said two-way circuits divide between said one-way circuits to be transmitted by one and dissipated in the other, and signalwaves trom the other of said two-way circults divide between said one-way circuits to be transmitted by said,

other one-way circuit and dissipated in said one one-way circuit, a one-way repeater in each of said one-way circuits, marginally operated means responsive to signal waves a in the output of the repeater in said'one one way olrcult to reduce the transmlssion efliciency of said'other one-way circuit when waves are being transmitted by said one oneway circuit, and when the energy level of waves from said other two-way .clrcult exceeds a certain level above thenormal signaling level, and marginally operated means similarly responsive to signal waves in the output of the repeater in-the other oneway circuit, 8. A'combination, accordlng to claim 7,

and having an output transformer forthe repeater in each one-way line, the output transformer having a primary winding connected tothe output circuit of the repeateig a secondary'winding' connected to the associated two-way transmission circuit and a tertiary winding, the marginally operated means responsive to waves in the output circuit of each repeater being connected to said tert ary winding.

9. A pair of one-way transmlssion lines, a vibrating relay responsive to Waves in one of said lines for reducing the efiiciency of transmission of said other line while waves are being transmitted by said first line, said relay maintaining its vibration .for'sufiicient time after the cessation of the transmission of waves in said first line to prevent the setting up of echo efi'ects.

In witness whereof, I hereunto subscribe my name this 31st dayof January, A. D. 1927.

a v HENRY W. ONEILL. 

